The present invention relates to an image scanner, in which an original placed on an original placing surface of a transparent plate is scanned by a scanning device that is disposed opposite to the original placing surface with respect to the transparent plate, irradiates the original with light by means of a light source and scans the reflected light from the original, and to an image scanning method.
In a known example of conventional image scanners, a platen made of transparent glass is attached to an upper portion of a box housing with the upper portion opened, and a scanning device, such as a Contact Image Sensor (hereinafter referred to as “CIS”), is reciprocably provided under the platen. In the image scanner, an original is placed on the platen with a surface to be scanned facing down, and an image on the original is optically scanned by using the CIS. Then, a resulting light signal is converted into an electric signal to create image data.
In such an image scanner provided with a CIS, there are differences in optical properties among light receiving elements, and unevenness in illuminance among individual light sources. This sometimes results in variation in scanned values that is undesirably large for creation of image information. It is, therefore, necessary to perform some correction of the differences in optical properties among light receiving elements and of the unevenness in illuminance among individual light sources prior to image scanning by the CIS.
Generally, scanning of a white plate or a white roller is performed with a light source turned off prior to image scanning by the CIS, and the resulting light signal is converted into an electric signal. The electric signal is stored in a buffer memory as black image data. Then, the correction of image data of an original is performed based on the black image data. This may compensate for differences in optical properties among light receiving elements.
Further correction is performed as disclosed in Publication of Unexamined Japanese Patent Application No. 2000-115473. Specifically, the light source of the CIS is turned on, and the reflected light obtained from the white plate or the white roller as a white reference is focused onto light receiving elements and is scanned. The resulting light signal is converted into an electric signal, and the electric signal is stored in a buffer memory as white image data. Then, the correction of image data of the original is performed based on the white image data. This may compensate for unevenness in illuminance among individual light sources.
The image scanner is provided with an original pressing plate for covering the platen during scanning of the original. The original pressing plate is arranged so as to be openable/closable in a vertical direction (i.e., in upper and lower directions). However, image scanning of a thick original, such as a book original, using the CIS is performed with the original pressing plate opened with respect to the platen, while the spine of the book original is pressed downward in order to prevent causing a shadow from the binding margin.